In a DNase footprinting experiment, either the template or...

In a DNase footprinting experiment, either the template or nontemplate strand can be end-labeled. In Figure 5.37a, the template strand is labeled. Which strand is labeled in Figure $5.37 b$ ? How do you know?

Key Concepts

DNase Footprinting

DNase footprinting is a technique used to identify the specific regions of DNA that are bound by proteins. In this assay, DNase I enzyme cleaves accessible regions of DNA, while sections protected by protein binding remain intact. The resulting pattern of cleaved fragments, when resolved on a gel, reveals a 'footprint' that corresponds to the protein-binding site.

End Labeling

End labeling is the process of attaching a detectable marker, such as a radioactive or fluorescent tag, to one end of a DNA molecule. This labeling allows for the visualization of DNA fragments after enzymatic digestion. The pattern observed on the gel depends on which strand is labeled, as only fragments containing the labeled end are detected, making it possible to infer details about protein-DNA interactions.

Template and Non-template Strands

In the context of transcription, the template strand is the one that is read by RNA polymerase for RNA synthesis, whereas the non-template (or coding) strand has the same sequence as the RNA transcript (except for thymine being replaced by uracil). In a DNase footprinting experiment, knowing which strand is labeled is crucial because the resulting fragment pattern will differ. By comparing the cleavage patterns and understanding that one strand was labeled in one part of an experiment, one can deduce which strand must be labeled in a complementary setup based on the symmetry and relative positions of the footprints.

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